Solving Equations with inputs from an Excel file

Hi, I am modelling a solar panel and I am struggling to get a solution for the Tpv shown in the code. When I use a single value for Ta there are no problems in finding an exact solution. However when I get the Ta to be read from the excel sheet (column 8, 24 rows) it returns me with no solutions (In the workspace Tpv is defined as "0x1 sym"). I have pasted my model below, any help would be greatly appreciated.

Hi, I am modelling a solar panel and I am struggling to get a solution for the Tpv shown in the code. When I use a single value for Ta there are no problems in finding an exact solution. However when I get the Ta to be read from the excel sheet (column 8, 24 rows) it returns me with no solutions (In the workspace Tpv is defined as "0x1 sym"). I have pasted my model below, any help would be greatly appreciated.

%% Energy balance Top layer

fileName1 = '1Day.xlsx';

numData1 = xlsread(fileName1);

Ta = numData1(:,8);



EtaG = 0.88; %emissivity of glass

Sigma = 5.67*10^-8; %stefan boltsman constant

Tsky = 0.0552.*Ta.^(1.5);

Tg = Ta + 10;

qsky = EtaG*Sigma.*(Tg.^4-Tsky.^4); %heat flux loss between sky and glass



Vw= numData1(:,12);

hwind = 4.5+2.9.*Vw;

qwind = hwind.*(Tg-Ta);



kair = 0.025;

eag = 0.005;

Etapv = 0.9;





syms Tpv

eqn1 = qsky + qwind == (Sigma .* (Tpv.^4 - Tg.^4)) / (1 / Etapv + 1/EtaG - 1) + (kair / eag) .* (Tpv - Tg);

Tpv= solve(eqn1,Tpv);

[Bob Thompson]

Is numdata1 populated?

[Alex Mcaulley]

Can you upload your data?

[rammah nagi]

Yes, I have attached the excel file to this

Answer 1

[Alex Mcaulley]

I suspect you have an overdetermined system (1 variable and 24 equations). Probably you want this:

%% Energy balance Top layer
fileName1 = '1Day.xlsx';
numData1 = xlsread(fileName1);

syms Tpv Ta Vw
% Ta = numData1(:,8);
EtaG = 0.88; %emissivity of glass
Sigma = 5.67*10^-8; %stefan boltsman constant
Tsky = 0.0552.*Ta.^(1.5);
Tg = Ta + 10;
qsky = EtaG*Sigma.*(Tg.^4-Tsky.^4); %heat flux loss between sky and glass
% Vw = numData1(:,12);
hwind = 4.5+2.9.*Vw;
qwind = hwind.*(Tg-Ta);
kair = 0.025;
eag = 0.005;
Etapv = 0.9;

eqn1 = qsky + qwind == (Sigma .* (Tpv.^4 - Tg.^4)) / (1 / Etapv + 1/EtaG - 1) + (kair / eag) .* (Tpv - Tg);
Tpv = solve(eqn1,Tpv);

res = double(subs(Tpv,{Ta,Vw},{numData1(:,8)',numData1(:,12)'})) %Where each column of res contains the solutions for each pair of values (Ta,Vw)

[rammah nagi]

Thank you for the help

[rammah nagi]

Say I wanted to use the values obtained from Tpv in another equation

qrpv= (Sigma * (res.^4 - Tg.^4)) / (1 / Etapv + 1/EtaG - 1);
qrpv1 = double(subs(qrpv,{Ta,Vw},{numData1(:,8)',numData1(:,12)'}));

Would this be the way to go about it?

[Alex Mcaulley]

Well, the correct way to do this is doing the substitution at the end (keeping the symbolic variables):

qrpv= (Sigma * (Tpv.^4 - Tg.^4)) / (1 / Etapv + 1/EtaG - 1);
qrpv1 = double(subs(qrpv,{Ta,Vw},{numData1(:,8)',numData1(:,12)'}));